Having high voltage and high capacity, a lithium secondary battery is widely used as a power supply for mobile phones, digital cameras, video cameras, notebook computers, electric automobiles and the like. In a lithium secondary battery in public circulation, a liquid electrolyte obtained by dissolving an electrolytic salt in a nonaqueous solvent is used as an electrolyte. Since the nonaqueous solvent includes many combustible solvents, the battery is provided with a safety mechanism.
For simplification of the safety mechanism, there has been proposed an all solid-state lithium secondary battery in which the electrolyte is formed from a solid material, that is, a so-called solid electrolyte material is used without using a nonaqueous solvent. It is reported in Japanese Unexamined Patent Publication No. 2008-103288 (Patent Document 1) that Li2S—P2S5 can be used for the solid electrolyte material of the battery.
The publication mentions a problem: hydrogen sulfide is generated in a battery in some cases such as when the solid electrolyte material is brought into contact with water in the air due to breakage of the battery or when the raw materials of the solid electrolyte material includes water, because the solid electrolyte material contains sulfur. The publication proposes prevention of leakage of the hydrogen sulfide generated to the outside of the battery by providing the exterior material of the battery with a hydrogen sulfide adsorbing material.